Report `ABSENT` when there is no value from ART.

This is an update to commit 3fb0c3e38b82ea65b65f6ee186098bed02d0809a.
The reason of this change is to avoid using `UNSPECIFIED (0)` in all
cases.

Bug: 423542133
Test: Presubmit
Flag: EXEMPT log only update
Change-Id: I124676faa8f65a9da80c17c0086d7ad04cd654a9
5 files changed